The invention relates to a process for opening the valves of valved bags to be filled with a bulk material, more particularly cement, and for engaging (inserting) the opened bags on a filling spigot.
The invention also relates to an apparatus for opening the valves of valved bags to be filled with a bulk material, more particularly cement, and for engaging the opened bags on a filling spigot of the machine. The apparatus comprises pivoting means for pivoting the valve-containing portion of the respective bag top into a position in which it is substantially perpendicular to the plane of the bag body. The apparatus has transfer means for transferring the bags to the filling spigot and, after the valve has been opened by appropriate means, for engaging the bags on the filling spigot.
The usual current way of packing fine-grained bulk material, such as cement, is by means of filling machines which usually have a number of filling spigots for introducing the material into a bag.
The bags usually used are valved bags made of a strong paper. The advantage of such bags is that they close automatically as filling proceeds, so that no special measures are needed to seal the bags at their top.
A valved bag of the above type comprises a top which, with the bag filled, forms the top end surface of the bag, a body forming the bag walls, a bottom which is at the other end of the body and which, with the bag filled, forms the bottom end surface of the bag.
Except for the valve at the top, which will be described hereinafter, the bag top and bottom are of very similar construction, both being substantially rectangular and both being formed at both their ends as an equilateral triangle whose base corresponds to the length of the narrow side of the rectangle, the apex of the triangle being disposed centrally of the longitudinal line of symmetry of the top or bottom directly at the bottom or top end point of the lateral fold of the bag body.
The main difference between the bag top and the bag bottom is that the bag top is open at one end so as to be able to receive the filling spigot of a filling machine. Since the top has a double-walled portion at this open area, the bulk material entering the bag through the spigot presses the bottom layer of this zone, known as the valve zone, against the overlapping top layer just before the bag has been completely filled, so that an adequate closure is provided.
In the empty state the bag top and bag bottom are each folded or engaged around their respective longitudinal line of symmetry -- hereinafter also called the bending edge of the bag top and the bending edge of the bag bottom respectively -- onto the bag body, so that the bag may be stored empty in a very reduced space and without being damaged. The bags are stored by being placed either one upon another or one after another or by being wound around a shaft or the like to form a roll or reel in which the individual bags are held together by two strips and also by frictional engagement. When needed for use they can readily be detached individually from the roll or reel.
The conventional manual procedure of opening the valve and engaging the bags on the filling spigots of filling machines needs substantial labor and is therefore expensive. A number of suggestions have therefore been made to mechanise this operation, particularly since the duration of operational steps in modern filling machines of both the in-line and roundabout kind is so reduced that they cannot be taken advantage of with manual operation, at least in cases in which a single operator has to deal with a number of spigots.
For instance, a process and apparatus of the kind described have been disclosed wherein a stack of bags placed horizontally one above another are raised from below by a lifter to a predetermined level so that the top bag of the stack can be picked up by a pickup head. The same has two laterally extending sliders which can be extended from the center of the bag towards its top and bottom so as to be introduced between the folding gaps which are present in the top and the bottom between the top and the body and between the bottom and the body. When in the raised position, one slider then pivots upwards through 90.degree. so that the bag assumes an L-shaped position, the bag already being some distance away from the top bag of the stack. The upwardly pivoted bag top is then introduced into a claw which engages briefly the body below the head to open the valve. The claw then removes the bag from the apparatus, while the bag bottom disengages from its slider so that the bag portion which is still horizontal drops down freely. The claw then pushes the bag onto the filling spigot, whereafter the claw can be released, that is, disengaged from the bag.
Since the above-described movements of the various elements then have to be performed in the reverse order, an elaborate and complicated control is necessary. Also, this complicated movement pattern means that a corresponding amount of time is taken for the individual cycle, and because of permissible accelerations and delays etc., there is a minimum non-improvable cycle time which has ceased to be adequate for the timings possible with present-day filling machines.
In practical operation, however, this known apparatus has been found to have the very serious disadvantage that as a bag is being picked up, the sliders often fail to engage in the folds, because a bag of this kind is not planar, but is an item for conveyance which is very difficult to handle -- at least in this way -- and which is wavy or bent in all directions. Since the pickup head sliders must, as it were very briefly, engage linearly below the corresponding portion of the top of the bag and the corresponding portion of the bottom of the bag, difficulties often occur because there is a bend or kink or the like in one of these portions. Also, operating difficulties arise when the bags are not disposed in an extended position and the bottom part of the bag has moved towards the top part or conversely.
To obviate these difficulties, it has been sought to accelerate the working cycle by simplifying the movement pattern and the number of structural elements, control elements and so forth has been reduced. By omitting the above-described sliders it has been sought to obviate the operating difficulties just described.
Accordingly, German Laid-Open Application (Offenlegungsschrift) No. 2,221,039 discloses an apparatus for automatically engaging bags on a filling spigot. The apparatus has a first pneumatic suction device which has suction cups and which raises vertically the top bag of a stack of bags stacked one above another in horizontal orientation; the suction cups of this first pneumatic suction device engage eccentrically the top surface of the body -- i.e., eccentrically towards the bag top -- so that the bag engaged by the suction cup pivots, when lifted from its horizontal position, into a vertical position.
A second suction device then moves the bag thus raised close to the filling spigot.